How to Detect if a User Is Idle

You are running a Windows forms application that runs as a system tray. You have a few notifications that you would like to show the user. However, what good are notifications if the user is away? He or she will not see them.

Solution

Run a timer that detects when the user is active on the machine, and then show the notification or other tasks that you would like to provide. Below is the sample code that will do this for you. Of course, for your production environment, you would use a timer of some sort or event subscription service.

I have tested this by using other applications while the program monitors my input. It's safe to say that it works across all of my applications, even when the screen is locked. You might want to deal with an issue where the screen is locked but the user is moving the mouse.

I know that MSDN mentions that GetLastInputInfo is not system wide. However, on my Windows 10 machine, it does seem to be the case that it is system-wide.

using System;
using System.Runtime.InteropServices;
using System.Threading;

namespace MyMonitor
{
 class Program
 {
 static void Main()
 {

 for (var i = 0; i < 1000; i++)
 {
 Console.WriteLine($"Last Input: {LastInput.ToShortTimeString()}");
 Console.WriteLine($"Idle for: {IdleTime.Seconds} Seconds");
 Thread.Sleep(TimeSpan.FromSeconds(1));
 }
 }

 [DllImport("user32.dll", SetLastError = false)]
 private static extern bool GetLastInputInfo(ref Lastinputinfo plii);
 private static readonly DateTime SystemStartup = DateTime.Now.AddMilliseconds(-Environment.TickCount);

 [StructLayout(LayoutKind.Sequential)]
 private struct Lastinputinfo
 {
 public uint cbSize;
 public readonly int dwTime;
 }

 public static DateTime LastInput => SystemStartup.AddMilliseconds(LastInputTicks);

 public static TimeSpan IdleTime => DateTime.Now.Subtract(LastInput);

 private static int LastInputTicks
 {
 get
 {
 var lii = new Lastinputinfo {cbSize = (uint) Marshal.SizeOf(typeof(Lastinputinfo))};
 GetLastInputInfo(ref lii);
 return lii.dwTime;
 }
 }
 }
}